For many years, Ethernet has been used as a LAN (Local Area Network) technology, and enterprises have managed these networks with the use of Internet protocols such as Simple Network Management Protocol (SNMP), ICMP Echo (or IP Ping), IP Traceroute, and Cisco Unidirectional Link Detection Protocol (UDLD). EOAM (Ethernet Operations Administration and Maintenance) is a set of protocols for installing, monitoring, and troubleshooting MANs (Metropolitan Area Network) and WANs (Wide Area network). The use of Ethernet as a networking technology has created the need for a new set of OAM protocols since there are now large and complex networks with a wide user base that involves different operators providing end-to-end services.
The IETF (Internet Engineering Task Force) develops and promotes Internet standards. The One-way Active Measurement Protocol [RFC4656] (OWAMP) provides a common protocol for measuring one-way metrics between network devices. OWAMP can be used bi-directionally to measure one-way metrics in both directions between two network elements. However, it does not accommodate round-trip or two-way measurements.
Two-Way Active Measurement Protocol (TWAMP) [RFC5357] provides a standards-based method for measuring the round-trip IP performance (packet loss, delay and jitter) between two devices. TWAMP uses the methodology and architecture of One-Way Active Measurement Protocol (OWAMP) to define a way to measure two-way or round-trip metrics.
There are four logical entities in TWAMP: the Control-Client, the Session-Sender, the Server, and the Session-Reflector. The Control-Client and Session-Sender are typically implemented in one physical device (the “Client”) and the Server and Session-Reflector in a second physical device (the “Server”) with which the two-way measurements are being performed.
The Control-Client and Server establish a TCP (Transmission Control Protocol) connection and exchange TWAMP-Control messages over this connection. When the Control-Client wants to start testing, the Client communicates the test parameters to the Server. If the Server agrees to conduct the described tests, the test begins as soon as the client sends a Start-Session message. As part of a test, the Session-Sender sends a stream of UDP-based (User Datagram Protocol) test packets to the Session-Reflector, and the Session-Reflector responds to each received packet with a response UDP-based test packet. When the Session-Sender receives the response packets from the Session-Reflector, the information is used to calculate two-way delay, packet loss, and packet delay variation between the two devices.
The ITU (International Telecommunication Union) is the United Nations specialized agency for information and communication technologies (ICTs). ITU standards (called Recommendations) are fundamental to the operation of ICT networks. ITU-T Y.1731 performance monitoring provides standards-based Ethernet performance monitoring that encompasses the measurement of Ethernet frame delay, frame delay variation, and frame loss and throughput.
IEEE 802.1ag IEEE Standard for Local and Metropolitan Area Networks Virtual Bridged Local Area Networks Amendment 5: Connectivity Fault Management is a standard defined by IEEE (Institute of Electrical and Electronics Engineers). It defines protocols and practices for OAM for paths through bridges and local area networks (LANs). It is largely identical with ITU-T Recommendation Y.1731. The standard:                Defines maintenance domains, their constituent maintenance points, and the managed objects required to create and administer them.        Defines the relationship between maintenance domains and the services offered by VLAN-aware bridges and provider bridges.        Describes the protocols and procedures used by maintenance points to maintain and diagnose connectivity faults within a maintenance domain.        Provides means for future expansion of the capabilities of maintenance points and their protocols.        
ITU Y.1731 and similar OAM standards (including but not limited to TWAMP) require an explicit negotiation between the Originator (Client) and the Reflector (Session-Reflector) to establish a unique Flow Identifier. This approach prevents a Test PDU (protocol data unit) from being processed by a multitude of Reflectors downstream from an Originator, as illustrated in FIG. 1.
Due to the need to explicitly generate different OAM sessions (one per pair of Originator and Reflector) in the current state of the art, it is not possible to generate a Test PDU from an Originator that can collect measurements from more than one Reflector at a time along a test path, even though the Test PDU may traverse said Reflectors in order to reach a remote Reflector.
FIGS. 2-4 are from the ITU Y.1564 standard and are used to illustrate the need for delay and other measurements needed to qualify an Ethernet circuit at installation. FIG. 2, from ITU Y.1563, illustrates the layered nature of the performance of the Ethernet service. This network is comprised of connection-oriented or connectionless links that are connected to bridges that will process the Ethernet Layer inside the network. Each time an Ethernet frame is going through an Ethernet layer, it will be processed for integrity and sent to the next bridge through a Lower Layer (LL) connection. Lower Layers are based on multiple technologies, for example, SDH, OTN, PDH, MPLS, ATM and ETY. The performance of all Ethernet Layers and Lower Layers will impact the end-to-end performance of the network used to deliver services.
Higher layers may be used to enable end-to-end communications. Upper layers may include protocols like IP, MPLS and Ethernet that allow a greater scalability for network deployment. Other protocols, like TCP, provide the capability to retransmit frames should a frame loss occur. Unfortunately, two of the drawbacks of TCP are added delay in the transmission of user information, and the possible limitation of maximum advertised window size and interaction with the bandwidth-delay product and flow control interaction with loss and delay of the Ethernet Service. The embodiment is able to perform the requested measurement independently from the fact that the links (or Lower Layer—LL) used to carry the Ethernet Virtual Circuits (EVC) may operate at Layer 2 or Layer 3.
FIG. 3, taken from ITU Y.1564, provides a simple example of Ethernet service areas and is referred to as an Ethernet service activation measurement. The goal of the test is to verify the configuration and performance of Ethernet-based services. The test verifies Ethernet Service Attributes including Committed Information Rate (CIR), Excess Information Rate (EIR) and other attributes. This shows the different portions of a network that support an Ethernet service instance.
It is further shown that the UNI reference point occurs in the middle of the access link, or more precisely that the UNI is a reference point whose functionality is split into customer (UNI-C) and network (UNI-N) components. From a service provider's perspective, they need to deliver services from UNI-C to UNI-C and it is from this perspective that the test methodology was created.
The CE (Customer Equipment) and the operator's network exchange service frames across the UNI, a service frame is an Ethernet frame transmitted across the UNI toward the Service Provider (called ingress service frame) or an Ethernet frame transmitted across the UNI towards the CE (called an egress service frame). Many services run on each UNI. They are qualified by their attributes:                Connection type        Traffic parameters: QoS (including VLAN information), traffic type (data vs. management), etc.        Bandwidth profile        Performance criteria: FD, FDV, Frame Loss ratio, availability, etc.        
From this, it is easy to see that an Ethernet Virtual Circuit may actually span multiple transport networks at Layer 2 or Layer 3. This creates challenges to efficiently measure delays and packet loss with traditional methods. The performance measurements can only be taken outside of the inner boundaries of the Transport Operator Network.
FIG. 4, from ITU-T y.1563, illustrates how Measurement Points (MP) are typically found at the boundaries between different Lower Layers used to support the EVC. The positioning of these MPs (or Reflectors) is critical to obtain adequate measurements. As per the above diagram, a 2-way delay measurement is typically taken from the SRC to the DST and back to the SRC and does not provide detailed delay information for each Exchange Link (or Lower Layer). The performance measurements can only be taken outside of the inner boundaries of the Network Section where MPs are addressable for the purpose of performance measurements.